This document provides installation instructions for an Aprilaire 550 whole-house humidifier. It states that a licensed professional should perform the installation. The instructions outline cutting openings in ducts to attach the humidifier housing and connect a duct to the bypass damper. Wiring must be done by a licensed professional and involves connecting the transformer to the furnace power source. Once installed, the humidistat and solenoid valve must be correctly wired and connected.